Optical power meters based on thermopile discs are well known in the art. Such discs are made of a heat conducting material, are heat-sinked at their periphery, and have a central absorber surface area on which the power to be measured impinges. A generally circular thermopile element is disposed near the outer edge of the disc surface, inward of the heat-sinked periphery, such that heat generated by the impinging beam flows outwards towards the cooled periphery, crosses the hot and cold junctions of the thermopile, and generates an integrated voltage across the ends of the thermopile proportional to the power falling on the absorber surface. An entrance aperture in the power meter head using such a disc limits the region of impingement of the beam to be the central absorber surface area.
In U.S. Pat. No. 4,964,735 to M. W. Sasnett et al., there is described a thermocouple laser power meter with the thermopile ring divided into four equal sectors giving a type of quadrant array. With the division of the thermopile into sectors, it becomes possible to measure the position of the laser beam by analysis of the comparative voltages generated in each sector of the thermopile, as well as the total power, by addition of all of the voltages from the sectors.
An important parameter regarding the laser beam itself is the beam size, as measured by any one of the parameters used in the art for such measurements. Power meters currently available are not able to provide a measure of this beam size. Beam size is an important parameter in applications involving the use of laser beams. Currently, a beam profiling instrument is generally required for performing such a measurement, and such a beam profiler is substantially more expensive for the user than a power meter.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.